This invention relates to a four-step method for preparation of perfluorinated vinyl ethers having sulfonyl fluoride end-groups according to the formula FSO2xe2x80x94(CF2)nxe2x80x94Oxe2x80x94CFxe2x95x90CF2, where n is 2-5, which are an important class of monomers in the synthesis of ion exchange resins.
U.S. Pat. No. 4,749,526 discloses preparations for fluoroaliphatic ether-containing carbonyl fluoride compounds by reacting a fluorinated carbonyl compound with hexafluoropropylene oxide in the presence of at least one catalyst selected from potassium iodide, potassium bromide, cesium iodide, cesium bromide, rubidium iodide and rubidium bromide.
U.S. Pat. No. 5,902,908 discloses a method for preparing a fluorinated vinyl ether by reacting a fluorinated carboxylic acid halogenide with a metal compound below the decomposition temperature for the corresponding metal salt in the absence of solvent and then raising the temperature of the produced corresponding metal salt above the decomposition temperature.
U.S. Pat. No. 6,255,536, incorporated herein by reference, discloses a process for the preparation of a perfluorinated vinyl ether of the formula CF2xe2x95x90CFxe2x80x94Oxe2x80x94Rf wherein Rf is a linear, branched or cyclic perfluorinated aliphatic group that may contain oxygen atoms hereby forming additional ether linkages.
Briefly, the present invention provides a method of making a perfluorinated vinyl ether having a sulfonyl fluoride end-group according to the formula FSO2xe2x80x94(CF2)nxe2x80x94Oxe2x80x94CFxe2x95x90CF2, where n is 2-5, comprising the steps of: a) fluorination of: 
to produce FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF; b) reaction of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF with hexafluoropropylene oxide (HFPO) to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF; c) reaction of FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF with a salt of a metal cation M+P, where p is the valence of M, to produce (FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P; and d) thermal cracking of FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CFxe2x95x90CF2.
It is an advantage of the present invention to provide a convenient and efficient method for preparation of perfluorinated vinyl ethers having sulfonyl fluoride end-groups according to the formula FSO2xe2x80x94(CF2)nxe2x80x94Oxe2x80x94CFxe2x95x90CF2, which uniquely adapted to the case where n is 2-5, and especially the case where n is 4, these species being important monomers in the synthesis of ion exchange resins. It is a further advantage of the present invention to provide a method for preparation of perfluorinated vinyl ethers having sulfonyl fluoride end-groups according to the formula FSO2xe2x80x94(CF2)nxe2x80x94Oxe2x80x94CFxe2x95x90CF2, where n is 2-5, which does not require the use of tetrafluoroethylene (TFE), with it""s associated hazards and difficulty.
Briefly, the present invention provides a method of making a perfluorinated vinyl ether having a sulfonyl fluoride end-group according to the formula FSO2xe2x80x94(CF2)nxe2x80x94Oxe2x80x94CFxe2x95x90CF2, where n is 2-5, comprising the steps of: a) fluorination of: 
to produce FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF; b) reaction of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF with hexafluoropropylene oxide (HFPO) to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF; c) reaction of FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF with a salt of a metal cation M+P, where p is the valence of M, to produce (FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P; and d) thermal cracking of FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CFxe2x95x90CF2. The value of n is 2-5, typically 3-4, and most typically 4. The value of p is typically 1 or 2, and most typically 1. The salt of a metal cation M+P is most typically Na2CO3.
Step a) involves fluorination of a sultone, which is a 4-7 member ring according to the formula: 
where n is 2-5, to produce FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF. Fluorination may be accomplished by any suitable means, but is most typically accomplished by electrochemical fluorination as described in U.S. Pat. No. 2,732,398, incorporated herein by reference.
Step b) involves reaction of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF with hexafluoropropylene oxide (HFPO) to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF. Step b) may be accomplished by any suitable means, but is typically accomplished by addition of HFPO to a solution of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF in a suitable polar solvent such diglyme. Typically, a catalyst is present. The catalyst is typically a fluoride catalyst, most typically KF. The reaction may be performed in the absence of any catalyst other than a fluoride catalyst. Typically, HFPO is added in a molar amount that does not exceed the molar amount of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF present. More typically, the molar amount of FSO2xe2x80x94(CF2)(nxe2x88x921)xe2x80x94COF present remains in excess of the molar amount of HFPO present by at least 10%, more typically 20%, and more typically 30%. Step b) may be accomplished by methods disclosed in copending U.S. patent application Ser. No. 10/322,254, filed on even date herewith, incorporated herein by reference.
Step c) involves reaction of FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COF with a salt of a metal cation M+P, where p is the valence of M, to produce (FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P. The valence p may be any valence but is typically 1 or 2 and most typically 1. M may be any suitable metal, but is typically selected from Na, K, Rb and Cs and is most typically Na. The anion of the salt is any suitable anion, but typically one that is not so basic as to remove the fluorine from the sulfonyl fluoride function. The salt of a metal cation M+P is most typically Na2CO3. Step c) is typically carried out in a polar solvent, such as glyme, diglyme, and the like. Step c) is typically carried out at elevated temperature, typically between 40 and 100xc2x0 C.
Step d) involves thermal cracking of (FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P to produce FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CFxe2x95x90CF2, after removal of solvent. Any heat source sufficient to raise the temperature of produce (FSO2xe2x80x94(CF2)(n)xe2x80x94Oxe2x80x94CF(CF3)xe2x80x94COOxe2x88x92)pM+P to its decomposition temperature may be used. Decomposition temperatures vary with reactants, but will typically fall between 160xc2x0 C. and 210xc2x0 C. Typically, any remaining solvent is removed prior to thermal cracking, typically by application of vacuum or reduced pressure. The product may then be collected, isolated and purified by any suitable means.
It will be appreciated that isolation and purification of reaction products may be desirable following one or more of the steps of the present method.
This invention is useful in the synthesis of perfluorinated vinyl ethers having sulfonyl fluoride end-groups, which are an important class of monomers in the synthesis of ion exchange resins.
Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.